In 1994, a team of scientists led by David Mckay began studying the meteorite ALH84001, which had been discovered in Antarctica in 1984. Two years later, the McKay team announced that ALH84001, which scientists generally agree originated on Mars, contained compelling evidence that life once existed on Mars. This evidence includes the discovery of organic molecules in ALH84001, the first ever found in Martian rock. Organic molecules—complex, carbonbased compounds—form the basis for terrestrial life. The organic molecules found in ALH84001 are polycyclic aromatic hydrocarbons, or PAH’s. When microbes die, their organic material often decays into PAH’s.
Skepticism about the McKay team’s claim remains, however. For example, ALH84001 has been on earth for 13,000 years, suggesting to some scientists that its PAH’s might have resulted from terrestrial contamination. However, McKay’s team has demonstrated that the concentration of PAH’s increases as one looks deeper into ALH84001, contrary to what one would expect from terrestrial contamination. The skeptic’s strongest argument, however, is that processes unrelated to organic life can easily produce all the evidence found by McKay’ s team, including PAH’s. For example, star formation produces PAH’s. Moreover, PAH’s frequently appear in other meteorites, and no one attributes their presence to life processes. Yet McKay’s team notes that the particular combination of PAH’s in ALH84001 is more similar to the combinations produced by decaying organisms than to those originating form nonbiological processes.
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主旨题
文章主要提出了DM队伍的研究，怀疑派提出怀疑，DM进行反驳
选项A new ways 文章结构未提及
选项B revise 与文章结构不符
选项c criticism 只是一味批判。没有反驳，
选项D concerning the origin of ALH84001错误。文章争论的是evidence，是pah
选项E controversy争论，有反驳，正确
选项 C 和 E 的区别在于，文章是在反驳这帮研究人员得出来的结论，还是反驳他们所使用的证据，即，是结论有问题(C)还是证据有问题(E)，这是这两个选项的区别。从文中得知，文章是对 PAH (即，证据)存疑，由于证据已经有问题了，所以得出的结论肯定不可信，选E。
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2020-12-18 16:19:16
c选项的为 present a criticism of an research ，可是呢，其第二段是对其第一段研究得出的结论的一个重要证据进行反驳 虽然C好像不错，但是远远比不上E，直接说出了文章结构：某研究得出结论---通过反对其中的某个证据----质疑结论的有效性
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2016-04-11 09:15:40
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